Electrolytic recording medium



May 13, 1969 LIEBLICH ELECTROLYTIC RECORDING MEDIUM Filed on. 27. 1966IN VEN TOR. /////V4 [/a'z/M United States Patent Int. Cl. 341m /20 US.Cl. 204-2 11 Claims This invention relates to the art of electrolyticrecording, and in particular to an improved electrolytic recordingmedium or paper.

Recording paper of the electrolytic type is generally marked by passingthe paper between a positive eroding metal anode electrode and anegative non-eroding cathode electrode. The paper is impregnated with anelectrolytically-conducting solution containing certain ingredients.When a voltage is applied between the electrodes and current is passedthrough the recording paper, metal ions are introduced into the paperfrom the anode and reacted with one or more of the ingredients of thepaper impregnant to form a colored mark on the recording paper.

To be acceptable for facsimile recording purposes, the recording paperpreferably should be white initially and should have the ability toproduce marks having a density which is at least close in linearrelationship to the current passed through the paper. The density of themarked area should be variable uniformly in a range from white for zerocurrent flow through grays for currents of intermediate magnitude toblack for currents of maximum value. The mark preferably should be blackso as to provide a good contrast with the white background.

There should also be a minimum of bleeding or fringing of the mark so asto provide good resolution. The unmarked paper while stored in moistcondition in sealed containers for extended periods of time prior to useshould remain stable without chemical decomposition of its ingredientswhich would cause discoloration of the paper or affect thereproducibility of results without recorder adjustment. Further, themarked recording paper should not become discolored, give off unpleasantor other odors, or be subject to the transfer of the mark to adjacentmaterials. The marked recording paper should be insensitive to lighteven after being repeatedly run through any of the conventionalduplicating machines involving exposure to ultraviolet or other stronglight sources.

Heretofore successful recording papers have been provided employingpyrocatechin, also called catechol, as the marking compound. Whilegenerally satisfactory, some difiiculty has been had with the catecholpapers because of the tendency of catechol to diffuse or transfer to andto discolor adjacent sheets of paper in contact with or in closeproximity thereto. Catechol vapors also may cause discoloration of thewalls and other surfaces near the recorder during the recordingoperation.

This invention provides an improved electrolytic recording medium whichis free from objectionable odors. Moreover, the mark produced on therecording medium of this invention is of high resolution and definitionwith minimal bleed or drag. The medium also shows markedly improvedvapor pressure and transfer and stability characteristics overcatechol-containing recording media.

The electrolytic recording medium of this invention, is

a porous sheet impregnated with an electrolytically-conducting solutioncontaining catechol oxalate (o-phenylene oxalate). This material givesan excellent blue to bluegreen mark when used as a marking compound inan electrolytic recording medium marked by the passage of currentthrough the sheet and contacting an anode which contains iron. The markis best obtained on a sheet in the acid pH range preferably betweenabout two to about four.

Although the aqueous solubility of catechol oxalate is only about 0.4g./ ml. of water, the solubility is significantly improved by theaddition of certain glycols, polyethylene glycols, and ether derivativesof polyethylene glycols. These additives act as solubilizers ordispersing agents, or both.

These and other aspects of the invention will be more fully understoodfrom the following detailed description and the accompanying schematicperspective drawing showing the recording system of this invention.

Referring to the drawing, a sheet of paper 10 impregnated with aconductive electrolyte containing catechol oxalate is passed between astationary eroding anode 11 which contains iron, and a rotatablenon-eroding cylindrical cathode 12 which has a prismatic platinum-Compound: Amount, g. Catechol oxalate 1.5 Trimethylene glycol 10.5Sodium nitrate 10.0

Water 85.0

The above solution had a pH of three and was sufiicient to impregnateten square feet of paper having high wet strength and a thickness ofabout three mils.

Ordinarily, the aqueous solubility of catechol oxalate at roomtemperature is only about 0.4 g./100 ml. of water, but its solubilitywas significantly increased by the addition of the trimethylene glycol.Other polyethylene glycols and ether derivatives of polyethylene glycolscan be used as solubilizers or dispersing agents, or both. For example,Tergitol NPX (a trade name for an ether of polyethylene glycol) is aneffective dispersant for catechol oxalate in aqueous solution, and thetrimethylene glycol (1,3 propanediol) is a particularly effectivesolubilizer.

The paper impregnated with the formulation of the above example produceda good blue to blue-green mark when subjected to a marking current asshown in FIG. 1. The contact area of the electrodes against therecording paper was about .0001 inch. The paper was about three milsthick when dry before impregnation, and about 3.5 mils thick afterimpregnation. The paper was impregnated by passing it through thesolution and permitting the impregnant to distribute itself evenlythroughout the paper. 'Excess impregnant was removed by passing thepaper between pressure rollers (not shown), so that when ready for usein the recorder, the impregnated paper had about twenty-five percent toabout fifty percent moisture by weight. To retard evaporation, theimpregnated paper was stored in suitable sealed containers until readyfor use.

The paper prepared and used in the recorder as just described produced agood mark of satisfactory optical density at a spot speed in the rangeof between about twenty-three to about 135 inches per second at avoltage between about forty to about one hundred volts with the currentflow in the range of milliamperes to about 260 milliamperes.

In the example given, the concentration of the catechol oxalate is shownas about 1.5%. However, the amount can be varied from a minimal quantityup to the maximum which can be dispersed or carried in solution by theuse of solubilizers.

It is desirable to keep the pH in the acid range for producing a mark ofhighest resolution and definition. Preferably, the pH should be betweenabout two and about four. The mark produced on the paper under theseconditions has minimal bleed or drag, and improved stabilitycharacteristics over catechol-containing recording media.

I claim:

1. An electrolytic recording medium comprising a sheet impregnated withan electrolytically-conducting solution containing at least 0.4 percentof catechol oxalate.

2. A recording medium according to claim 1 in which the pH of thesolution of catechol oxalate is between about two and about four.

3. A recording medium according to claim 1 in which the solutionincludes a solubilizer for the catechol oxalate.

4. A recording medium according to claim 3 in which the solubilizer is aglycol.

5. A recording according to claim 4 in which the solubilizer istrimethylene glycol.

6. A recording medium according to claim 1 in which the solutionincludes a dispersant for the catechol oxalate.

7. A recording medium according to claim 6 in which the dispersant is apolyethylene glycol ether.

8. An electrolytic recording system comprising a sheet 2 impregnatedwith an electrolytically-conductive solution containing at least 0.4percent of catechol oxalate, an

iron-containing anode in contact with one part of the sheet, and acathode in contact with another part of the sheet so that an electriccurrent can be passed through the electrolyte to change its color whereit is contacted by the anode.

9. A system according to claim 8 in which the ironcontaining anode ismade of stainless steel.

10. A system according to claim 8 in which the electrolytic solution hasa pH between about two and about four.

11. A system according to claim 8 in which the solution includes asolubilizer for enhancing the water solubility of the catechol oxalate.

References Cited UNITED STATES PATENTS 2,358,839 9/1944 Wagner 204-22,692,228 10/1954 Clancy 2042 2,953,505 9/1960 Mones 2042 2,995,5018/1961 Tucker et a1. 2042 JOHN H. MACK, Primary Examiner.

T. TUFARIELLO, Assistant Examiner.

1. AN ELECTROLYTIC RECORDING MEDIUM COMPRISING A SHEET IMPREGNATED WITHAN ELECTROLYTICALLY-CONDUCTING SOLUTION CONTAINING AT LEAST 0.4 PERCENTOF CATECHOL OXALATE.